An anisotropically conductive elastomer sheet is a sheet exhibiting conductivity only in its thickness-wise direction or having pressure-sensitive conductive conductor parts exhibiting conductivity only in the thickness-wise direction when they are pressurized in the thickness-wise direction. As such anisotropically conductive elastomer sheets, there have heretofore been known those of various structures.
As anisotropically conductive elastomer sheets exhibiting conductivity only in the thickness-wise direction in a non-pressurized state, there have been known, for example, those obtained by arranging conductive fiber in a sheet substrate composed of insulating rubber in a state oriented so as to extend in the thickness-wise direction, and those (see, for example, the following Prior Art. 1) obtained by alternately laminating conductive rubber with carbon black or metal powder incorporated therein and insulating rubber in a plane direction thereof.
On the other hand, as anisotropically conductive elastomer sheets exhibiting conductivity only in the thickness-wise direction when they are pressurized in the thickness-wise direction, there have been known those (see, for example, the following Prior Art. 2) obtained by uniformly dispersing metal particles in an elastomer, those (see, for example, the following Prior Art. 3) obtained by unevenly distributing particles of a conductive magnetic substance in an elastomer, thereby forming a great number of conductive parts each extending in a thickness-wise direction thereof and an insulating part mutually insulating them and those (see, for example, the following Prior Art. 4) obtained by defining a difference in level between the surface of each conductive part and an insulating part.
Since such an anisotropically conductive elastomer sheet has such features that compact electrical connection can be achieved without using any means such as soldering or mechanical fitting, and that soft connection is feasible with mechanical shock or strain absorbed therein, it is widely used as a connector for achieving electrical connection between a circuit device, for example, a printed circuit board, and a leadless chip carrier, liquid crystal panel or the like in fields of, for example, electronic computers, electronic digital clocks, electronic cameras and computer key boards.
On the other hand, in electrical inspection of circuit devices such as semiconductor integrated circuit devices such as packaged IC and MCM, wafers, on which integrated circuits have been formed, and printed circuit boards, an anisotropically conductive elastomer sheet is used as a connector for achieving electrical connection between electrodes to be inspected formed on one surface of a circuit device, which is an object of inspection, and inspection electrodes formed on the surface of a circuit board for inspection.
In this electrical inspection of the circuit device, a test of direct current characteristics for measuring a source current, input-output voltage, input-output current and the like in the circuit device, a test of alternating current characteristics for measuring a propagation delay time between input and output terminals, transition time of an output waveform, maximum clock frequency and the like in the circuit device, or the like is conducted.
With the demand for speeding-up of processing in an electronic apparatus such as a computer, in resent years, a device having a high clock frequency has been used as a circuit device such as CPU installed in the electronic apparatus. In order to conduct the expected test of alternating current characteristics without causing a misfunction in electrical inspection of such a circuit device, it is important to sufficiently control noises to high-frequency signals.
As a means for controlling the noises to the high-frequency signals in an anisotropically conductive elastomer sheet used in the electrical inspection of the circuit device, there has been proposed a means for supporting the anisotropically conductive elastomer sheet by a frame plate having conductivity and connecting the frame plate to a ground (see, for example, the following Prior Art. 5 and Prior Art. 6).
However, according to such a means, it is difficult to sufficiently control the noises to the high-frequency signals when electrical inspection is conducted as to a circuit device having a clock frequency of, for example, at least 1 GHz.
Prior Art. 1: Japanese Patent Application Laid-Open No. 94495/1975;
Prior Art. 2: Japanese Patent Application Laid-Open No. 93393/1976;
Prior Art. 3: Japanese Patent Application Laid-Open No. 147772/1978;
Prior Art. 4: Japanese Patent Application Laid-Open No. 250906/1986;
Prior Art. 5: Japanese Patent Application Laid-Open No. 2000-164041;
Patent Art. 6: Japanese Patent Application Laid-Open No. 2002-33358.